This work centers on the elucidation of the mechanisms by which interferon alpha initiates the transcription of a number of genes. The mechanism, termed "signal transduction", is thought to occur by the rapid phosphorylation of protein kinases and their subsequent targeting of downstream proteins. This cascade ultimately involves the tyrosine phosphorylation and binding of a variety of transcription factors to DNA regions, and the productions of new proteins. With interferon, the events that occur post-signalling (ie protein induction, etc.) can ultimately be described in terms of antiproliferation and antiviral activity. I have found that in primary human lymphocytes that the antiproliferative but not antiviral activity of interferon alpha is mediated by the tyrosine kinase ZAP70, a protein intimately involved in T-cell receptor signalling and leukemia progression. The mechanism by which this occurs is currently being elucidated, but now appears to be centered on the induction of MAP kinase activity. I have developed a novel technique to "fingerprint" the tyrosine and serine phosphorylations caused by any cytokine or growth factor. The use of this technique is multi-faceted in that it can be used to identify and charactierize novel signaling molecules and pathways and at the same time be used as new and powerful bioassay for an identity test for any particular lot or manufacturing form of any cytokine from a product characterization read-out. The investigation of the mechanisms by which interferon alpha and other cytokines transduce their signal enables a broad understanding of cytokine gene regulation. This understanding is critical in forming science-based decisions on reviews of documents submitted to the agency and in particular to the Division of Cytokine Biology to support the INDs and PLAs. Additionally, the development of the two-dimensional phosphorylation fingerprint technique to identify novel signaling pathways has direct impact on the use of this technique for product characterization and a new type of bioassay for all cytokines and growth factors.